Generally, the prospect of a relay station (RS) in a next generation wireless communication system is very encouraging. The concept of the relay station (RS) is schematically explained as follows.
First of all, IEEE (institute of electrical and electronics engineers) 802.16 continues to progress with a standardization project of a new subject called a multi-hop relay after publishing IEEE 802.16-2004 as a standard specification targeting a fixed subscriber mobile station and IEEE.16e-2005 as a standard specification to provide mobility of a subscriber mobile station.
This project, which is taken care of by Task Group j (IEEE 802.16j) in IEEE 802.16, starts full discussions on usage models, relevant terminologies and technical requirements in the 2nd meeting in July 2006 since the 1st official meeting in May 2006. In the following description, IEEE 802.16 task group will be abbreviated 802.16j.
The concept of a relay station, which will be explained in the following description, may be used as the substantially identical concept for a relay station currently considered by 3GPP LTE-A system. And, a relay station capable of performing a same or similar function in one of various wireless access systems may be usable for the concept similar to that of a relay station according to the present invention.
PAR (project authorization request) of 802.16j is the standardization task to progress in the future and intends to achieve two kinds of objects including coverage extension of a service area and throughput enhancement.
Relay stations can be primarily categorized into two types. There are a relay station of a transparent type and a relay station of a non-transparent type. The transparent relay station has all operations and functions exist therein to manage a mobile station, while the non-transparent relay station plays a role in relaying all operations and function between a macro base station and a mobile station via the macro base station.
In aspect of a mobile station, a transparent relay station and a non-transparent relay station are treated as a single macro base station to have no change of operations but the mobile station may have a function of identifying a relay station and a macro base station from each other.
A network including a relay station may include a base station (BS), a relay station (RS) and a mobile station (MS). Despite being located outside a cell area of the base station, the mobile station is able to receive a radio signal via the relay station. And, it may be able to set up a path of high quality, which has a high-level adaptive modulation and coding (AMC) scheme, for the mobile station located within the cell area of the base station via the relay station. Hence, a user is able to obtain such an effect as increasing overall system capacity with the same radio resource.
The standard specification prepared by the 802.16j project has prescribed requirements. For instance, a mobile station, which is implemented on the bases of the previous 902.16-2004 and 802.16e-2005 specifications, should be able to communicate with a base station without any additional function. Hence, in a previous system, an application rage of a relay station may be limited in a manner of adding partial functions of controlling a relay station to the relay station itself and a previous base station. And, it is expected that specifications for a relay station become a core matter of the future standardization.
A relay station can be regarded as a sort of a subscriber mobile station that performs operations of a physical layer and a medium access control layer. Although the relay station is mainly controlled by a base station, it may have a prescribed control function of itself if necessary. As currently discussed utility models, relay stations of various types (e.g., a fixed relay station, a mobile relay station to provide a temporary service for a specific area, a relay station installable at a vehicle, a subway and the like, etc.) are currently taken into consideration.
The representative technical issues, which will be discussed, can be summarized as follows.
1. Procedure for a base station to identify relay stations existing within its area and to obtain and maintain information on a topology of connection with the identified relay stations
2. Definition of a physical transmission frame between a mobile station having backward compatibility with a previous IEEE 802.16 system and a relay station
3. Signal procedure to provide mobility between relay stations or between a relay station and a base station
4. Procedure for network entry of a relay station into a base station and entry procedure of a mobile station via a relay station
Meanwhile, a frame structure used by a relay station may include a downlink frame structure and an uplink frame structure. In particular, the downlink frame structure may include a downlink (DL) access zone and a downlink (DL) relay zone and the uplink frame structure may include an uplink (UL) access zone and an uplink (UL) relay zone.
In this case, if a single relay station exists between a base station and a mobile station (i.e., 1-hop structure), a DL access zone indicates an interval for a relay station (ARS) to transmit a data packet and the like to a mobile station (AMS) or another subordinate relay station and a UL access zone indicates an interval for a mobile station (AMS) or a subordinate relay station to transmit a data packet and the like to a corresponding relay station (ARS). In a DL relay zone, a relay station (ARS) is able to receive a data packet from a base station (ABS). In a UL relay zone, a relay station (ARS) is able to transmit a data packet to a base station (ABS).
A data packet may have a configuration of MAC PDU (medium access control protocol data unit). The MAC PDU is accompanied with a MAC header. Prior to the description of the MAC header, a protocol layer model defined in a general broadband wireless access system is described as follows.
FIG. 1 shows a protocol layer model defined in a wireless mobile communication system based on the generally used IEEE 802.16 system.
Referring to FIG. 1, a MAC layer belonging to a link layer may consist of 3 sublayers. First of all, a service-specific convergence sublayer (CS) is able to transform or map external network data received via a CS service access point (SAP) to MAC SDUs (service data units) of a MAC common part sublayer (CPS). In this layer, a function of discriminating SDUs of the external network and then linking a corresponding MAC service flow identifier (SFID) and a CID (connection identifier) to each other can be included.
The MAC CPS is the layer of providing such a core function of MAC as a system access, a bandwidth allocation, a connection establishment and management and the like and receives data classified by a specific MAC connection from various CSs via the MAC SAP. In doing so, QoS (quality of service) may be applied to data transmission via a physical layer and scheduling.
A security sublayer is able to provide an authentication function, a security key exchange function and an encryption function.
The MAC layer is a connection-oriented service and is implemented with a concept of transport connection. When a mobile station is registered to a system, a service flow can be provided by a negotiation between the mobile station and the system. If a service requirement is changed, a new connection can be established. In this case, the transport connection defines a mapping between peer convergence processes that use the MAC and the service flow and the service flow defines QoS parameters of MAC PDU exchanged in the corresponding connection.
The service flow on the transport connection plays a core role in managing a MAC protocol and provides mechanism for the QoS management of uplink and downlink. In particular, service flows can be combined with a bandwidth allocation process.
In a general IEEE 802.16 system, a mobile station can have a 48-bit universal MAC address at each radio interface. This address uniquely defines the radio interface of the mobile station and may be used to establish a connection of the mobile station in an initial ranging procedure. Since a base station verifies mobile stations with different identifiers (IDs) of the mobile stations, respectively, the universal MAC address may be used as a part of an authentication process.
Each connection can be identified by a connection identifier (CID) having a 16-bit length. While initialization of a mobile station is in progress, 2 pairs (e.g., UL & DL) of management connection are set between the mobile station and a base station and 3 pairs including the management connection can be optionally available. In a current IEEE 802.16m system, CID is replaced by a station identifier (STID) and a flow identifier (FID) for identifying a flow. In this case, the station identifier means a 12-bit identifier allocated to a mobile station performing a network entry (or network re-entry) by a base station and the flow identifier means a 4-bit identifier for identifying a connection (e.g., a management connection, a transport connection, etc.) for a specific mobile station. And, ARS STID can be assigned to an advanced relay station (ARS) of the IEEE 802.16m system.
In the above-described layer structure, a transmitting stage and a receiving stage may be able to exchange data or control messages via MAC PDU. In order to generate this MAC PDU, a base station or a mobile station may have a MAC header included in the MAC PDU.
In particular, the MA PDU may be able to include a MAC header, an extended header and a payload. The MAC header is always included in the MAC PDU, while the payload may be optionally included in the MAC PDU if necessary. Yet, the extended header is not included in the MAC PDU without the payload.
In the following description, a structure of a generic MAC header is explained with reference to FIG. 2.
FIG. 2 shows one example of a structure of a generic MAC header (GMH) or an advanced generic MAC header (AGMH) applied to IEEE 802.16m system.
Fields included in the MAC header shown in FIG. 2 are described as follows.
First of all, a flow identifier (Flow ID) field is ale to indicate a flow connection identifier of a generic MAC header. An extended header (EH) field indicates whether an extended header is accompanied behind the MAC header. A length field indicates a size of a payload accompanied behind MAC PDU or MAC header.
When data is transmitted using 2-byte GMH shown in FIG. 2, whether an extended header is accompanied can be indicated via the EH field and additional header information may be included via the extended header.
A relay station exchanges data with another relay station, a base station and/or a mobile station by a relay MAC PDU transmission and/or a MAC PDU transmission. In this case, in aspect of a relay station (ARS), the MAC PDU may mean a transmission unit including data transmitted to the relay station (ARS) and the relay MAC PDU may mean a transmission unit including data that the relay node should relay to another entity (e.g., data received from a base station and then relayed to a mobile station).
In doing so, the demands for a relay MAC PDU structure for a relay station, which relays data exchanged between a base station and a plurality of mobile stations, to perform more efficient data transmission on the base station and a data transmitting method using the same are rising.